Energy saving and emission reduction is a trend in the process of globalization and in the communications field, power conversion efficiency is an important aspect. The high efficiency of a power supply relies on both improvement of a power device and application of a power supply topology.
In order to improve the power conversion efficiency, in the prior art, manufacturers in the industry derive various improved bridgeless Power Factor Correct (PFC) circuits from conventional bridgeless circuits. FIG. 1 shows a bridgeless PFC circuit in the prior art, in which, L01 and L02 are inductors for a Switching DC (Boost) circuit, S01 and S02 are main switch tubes for the PFC circuit, D01 and D02 are commutation diodes for a Boost power supply, D03 and D04 are freewheeling diodes, D05 and D06 do not join in normal work and only function in surge protection through the work mechanism as follows.
In a positive semicircle, S01 is turned on, such that the inductor L01 is charged through a power supply passing S01 and D04; and when a current reaches a set value, S01 is turned off, a power supply of L01 is reversed, and L01 is connected to the power supply in series, so as to charge an energy-storage capacitor through D01 and D04, and transfer energy to a subsequent converted power supply. When an inductive current of the power supply decreases to a set value, S01 is turned on again to charge the inductor L01 to store energy again, and a cycle is repeated in this manner. In the positive semicircle, S02, D02, D03, and L02 do not work.
In a negative semicircle, S02, D03, and L01 work symmetrically with S01, D04, and L02 respectively, and work principles are the same as those in the positive semicircle. In the negative semicircle, S01, D01, D04, and L01 do not work.
With respect to circuit loss, for example, in the positive semicircle, in the stage of turnon and energy storage, the current flows through three devices L01, S01, and D04 in series; and in the stage of cutting off energy transfer by the switch tube, the current flows through three devices L01, D01, and D04 in series.
However, in the prior art above, the diodes D01 and D02 used on bridge arm are silicon carbide diodes which are costly, leading to a high cost of the whole bridgeless PFC circuit.
Next, due to a high voltage drop of the silicon carbide diode, more energy is lost when the current flows through D01 or D02 in series, so the power conversion efficiency is lowered.